Getter operating at various temperatures to occlude various gases



Jan. 26, 1965 R. w. GRIESSELY 3,167,673

GETTER OPERATING. AT VARIOUS TEMPERATURES TO OCCLUDE' VARIOUS GASESFiled June 19, 1961 FIGJ.

.I NVENTOR! RICHARD W. GRIESSEL,

BY l

IS ATTORNEY 3,167,673 GETTER QPE RATING AT VAREGUd TElllPERA- TUBES@CQLUDE VARTSUS GASEd Pdchard W. Griessel, Albany, N.Y., assignor toGeneral Electric (Iompany, a corporation of New York Filed lune 19,19e1,Ser. No. 118,164 all Claims. (Cl. 313-186) This invention relatesgenerally to gettering devices and pertains more particularly to anindependently controlled gettering device for an evacuated chamber.

While for many purposes a chamber can be evacuated by mechanical meansto an extent adequate for such purposes, some chambers such as theenvelope of an electron discharge device require a higher degree ofvacuum than can be obtained by the usual mechanical devices. It hasbecome common practice in industry to include within the envelope ofsuch a device a so-called getter material which will sorb or getter thegas molecules which may be left within the envelope after evacuation orwhich may be subsequently released from the structures within theenvelope. Often the getter material is selected from the materialsincluded in Group IV of the Periodic Table which includes, for example,titanium, zirconium and hafnium.

As is Well known, gas-sorbing capacities of these getter materials, andthus the rates at which these getter materials are effective to sorbgases, are enhanced when the materials are heated. This heating of thegetter material can be effected by placing it adjacent a normally heatedelement in the device to be evacuated or, alternatively, an independentgetter heating element can be provided which can be controllablyenergized at intervals during the life of the device.

It is an object of this invention to provide an improved getteringdevice the action of which can be controlled as desired.

it is also an object of this invention to provide a ge tering devicewhich will effectively sorb gases which tend to be sorbed at hightemperatures as well as gases which tend to be sorbed at lowertemperatures.

it is a further object of this invention to provide a gettering devicewhich will effectively sorb a plurality of gases, each of which may tendto be best sorbed at a distinct dilferent temperature.

Briefly stated, in carrying out the objects of this invention in oneform, a getter structure is provided in which a heater element ispositioned within a chamber to be evacuated. A getter element comprisinga first cylinder of gettering material is provided in the structure andis positioned about this heater so as to be heated thereby when theheater is energized. Another getter element comprising a second cylinderof gettering material is included in the structure and is positionedabout the first cylinder so that the second cylinder is thermallyshielded from the heater and will therefore be heated to a lowertemperature than the first cylinder. The outer cylinder can be longerthan the inner cylinder for thus disposing a section thereof moreremote, and thus more thermally isolated, from the heater contained inthe first cylinder. As an alternative form the heater can comprise aplurality of independently controllable sections with one heater sectionessentially determining the temperature of the inner cylinder and theother heater section essentially determining the temperature or" theextending section of the outer cylinder. In another alternative form theouter cylinder can be replaced by a plurality of axially spacedwasher-like elements of gettering material and which are adapted forhaving portions thereof varying in temperature in accordance with theradial distance from the inner cylinder. Additionally, the washer-likeelements can be provided with cylindrical outer rim portions efiectivefor iiiiild'ild Patented Jan. 26, 1965 minimizing radiated heat lossthereby to conserve power and for serving to minimize outward migrationto other elements in the device of volatile gettering material.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which:

FIGURE 1 is a schematic perspective and partially cut away view of agetter structure embodying one form of this invention;

FIGURE 2 is a schematic sectional view of a gettering device constructedin accordance with a second embodiment of this invention; and

FIGURE 3 is a schematic elevation of a gettering device constructed inaccordance with a third embodiment of the invention.

Referring now to FIGURE 1, a gettering device is illustrated which ismounted upon a supporting ring ltl. Fixed to the supporting ring ill andextendin" upwardly from it are a plurality of supporting legs 11. Anelongated inverted cup-shaped member 12 formed of gettering material issecurely mounted at the upper ends of the supporting legs 11. It hasbeen found that titanium, hafnium, and zirconium, or materialscomprising one or more of these metals, are particularly suitable foruse as gettering materials in this invention; however, other metals inGroup IV of the Periodic Table may be efficaciously used for someapplications. in addition to the use of these metals in a substantiallypure state, alloys, for example, of the type disclosed in US. Patent No.2,926,981 of V. L. Stout et 211., issued March 1, 1960 and assigned tothe same "assignee as the present invention are usable for some purposesin the application of this invention. A second elongated invertedcup-shaped member 113, also formed of suitable gettering material ispositioned in the cup-shaped member 12. The member 113 can be securelymounted in the described position in any suitable manner. For example,it can be mounted on the inner wall of the member 12. However, if thismanner of mounting is employed, it should be carried out by use of meanswhich will minimize heat transfer between the cup-shaped members l2 and13. It may be desirable to have the outer cup-shaped member 12 have sideWalls of greater length than the inner cup-shaped member 131 in themanner shown, and for some purposes it may be found preferable to makeboth cup-shaped members 12 and 13 of the same gettering material. Ahelical coil heater element 14 is positioned within the inner cup-shapedmember 13 and is electrically and mechanically secured at the top to asupporting and conducting rod 15. The rod 15 may be secured to thesupporting ring 7.63 by a plurality of radial braces 16.

In accordance with the invention, the heater element 14 is so positionedas to heat, directly by radiation, the inner cup-shaped member 13. Thislocation of the heater element 1% within the inner cup-shaped member 13shields the outer cup-shaped member 12 from the higher temperaturesexperienced by the inner cup-shaped member 13, and, thus, the outermember 12 is adapted for operating at a relatively lower tem eraturethan the inner iember 13. Also, when the outer member is longer than theinner member, the outer member includes a section portions of which arerelative progressively more remote from the heater than the inner member13 and the upper section of the inner member which is coextensive withthe inner member. In this manner the outer member is adapted forgradient progressively lower temperatures toward the lower end of thedevice.

The described arrangement therefore makes possible the use of a singleheater to achieve a substantially Wide range of different temperaturesin two getter members. The reason for desiring different temperatures intwo getter members arises from the nature of the gettering 1 ca process.While most of the active gases will be gettered at temperatures ofapproximately 700 C. and above, hydrogen will be released by the getterat these temperatures. To sorb hydrogen, the gettering material shouldbe at temperatures of approximately 400 C. or below. The structure ofthis invention therefore solves the problem of soroing substantially allthe gases (except noble gases) by maintaining one getter member at arelatively high temperature whereby it will sorb all the gases 67tcepthydrogen and will tend to emit any hydrogen previously sorbed, and asecond getter member at a lower temperature at which the hydrogen willbe effectively sorbed.

Referring now to FIGURE 2, a second embodiment of this invention will bedescribed. A longitudinally extending helical coil heater 2a ismechanically and electrically secured at the lower end to a supportingrod 21. Positioned around the heater coil is a cylindrical getter member22 which can be formed of the same material as either of theabove-described members 12 and 13 in PEG- URE l. Secured in axiallyspaced and stacked relation around the cylindrical getter member 22 area plurality of annular or washer-like elements 23 formed of a getteringmaterial of the same type as those described above. Botl the gettercylinder 22 and the washer-lilac ge' er elements 23 will become heatedwhen the coil heater 2b is energized; however, it can be readily seenthat the getter elements 23 will be heated to a lesser temperature hairthe getter cylinder 22 and the elements 23 will vary in temperature inaccordance with the radial distance of any portion thereof from theheater. Suitable supporting means 2d may be provided to maintain theheater coil and the two getter members in their proper physicallylocated and electrically insulated relative positions. Additionally, thewasher-like elements 22 can be provided with cylindrical outer rimportions 23a which are shorter in axial length than the space betweenadjacent ones of the elements 23. Thus, the rims 311 are adapted bothfor minimizing radiated heat, and thereby conserving energy, andforminimizing outward migration of volatile gettering material whichWouldtend to deposit undesirably on adjacent elements. However, the rims23a, because of the spacing between each one the cot and the nextadjacent element 23, allow access to gases to be sorbed to the outersurface of the cylinder 22 and the surfaces of the elements 23. i

As was previously described in connection with PEG- URE 1, both thegetter cylinder 22. and the, getter elements 23 may be of the samematerials or of different materials dependin upon the application towhich the device is to be put. In addition, the materials andtemperatures mentioned as being suitable for the embodiment of FIGURE 1may also be utilized for this embodiment,

of the invention.

Referring next to FIGURE 3, a third embodiment of this invention isdisclosed which will now be described. In this embodiment the variouselements can be supported in any desirable manner, such as thatillustrated in FIG- URE 1, and, therefore, no specific supporting meansis illustrated to simplify disclosure. An outer cylindrical gettermember 30 encloses an inner cylindrical getter member 31 together with asplit, or double-sectioned, helical coil heater element having an upperhalf 32 and a lower half 33. A cap member 34 of getter material can beprovided and positioned over the inner cylindrical getter member 31, Thetop of the upper half 32 of the split heater is electrically andmechanically connected to the top of a conducting, supporting rod 35.Provision is made for electrically connecting only the upper half 32 ofthe split heater by utilizing a center tap terminal 36 and thesupporting rod terminal 3'7 or for connecting the entire length of theheater by utilizing the terminal 33 of the lower half of the splitheater 33 and the supporting rod terminal 37. In the structure disclosedin FIGURE 3, the upper and lower sections 32 and 33, respectively, of

dthe heater can be selectively energized separately or jointly forcontrolling selectively the heating or" the getter members thereby toprovide different temperature for the above-discussed reason ofobtaining sorption of different active gases.

It will be understood, that in each of the embodiments of the inventionherein described, temperature gradients will exist along the dimensionsof the getter members, with the higher temperatures being those nearerthe heater, rather than only two specific temperatures resulting. Thisresult is desirable since gases gettered at the higher temperatures tendto difiuse through the metal to the cooler areas as the concentration ofsorbed gas increases, even though these gases would not be sorbedinitially at these cooler temperatures. The effect of the temperaturegradient is therefore to increase the gettering ability or capacity fora given mass of material and to provide optimum getter temperature forsorption of hydrogen as well as other gases.

Temperature gradients which cover a greater over-all range oftemperature can also be achieved by the addition of further gettermembers with possible additional heater elements. This idea is carriedout in the embodiment of the invention which has been shown in PEGUREThe invention herein disclosed may be utilized, as has been previouslyindicated, Within the main body of the envelope of an electron dischargedevice (not shown) or, if desired, as an appendage to the envelope.Inasmuch as this getter device is independently heatedand does notdepend upon the functioning of a discharge device, as do the so-calledparasitic getters or ones which rely upon heat from the cathode heater,its positioning in an existing vacuum tube design can be made with aminimum of redesigning of the electrode elements. Furthermore, as willbe understood from the foregoing, this invention is equally well'suitedto many other types of uses where a high vacuum is desired and notsolely to use in connection with electron discharge devices.

While particular embodiments of getter devices ern-.

ploying this invention have been shown and described, it will beunderstood from the foregoing that changes and modifications can be madeWithout departing from the spirit of the invention and'the scope of theappended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A getter device comprising in combination, a plurality of gettermembers, an independent heater element for said getter members, one ofsaid getter members interposed between said heater element and anotherof said getter members in heat shielding relationship thereto wlie 'ebysaid one getter member will be heated to a higher temperature than saidother getter member to getter a gas not gettered by said other gettermember at a lower temperature.

2. A getter device comprising 7 getter member, an independent heaterelement for said first getter member and closely adjacent thereto, asecond getter member interposed in heat shielding relationship betweensaid first getter member and said heater, whereby said second gettermember will be heated to a substantially higher temperature than saidfirst getter member to getter a gas not gettered by said first gettermember at a lower temperature.

3. A getter device according to claim 2, wherein said getter memberscomprise a metal selected from the group consisting of titanium,hafnium, and zirconium and combinations thereof.

4. A getter device comprising a longitudinally extending heater element,a first tubular getter member posi tioned around said heater element andcoextensive therewith, and a second tubular getter member positioned incombination, a first around said first getter member and longer thansaid first getter member.

5. A getter device comprising a supporting structure, a longitudinallyextending heater element mounted on said supporting structure, a firstinverted cup-shaped getter member coextensive with and positioned oversaid heater element, and a second inverted cup-shaped getter memberpositioned over said first cup-shaped getter and having longer sidewalls than the side walls of said first getter member.

6. A getter device comprising a supporting structure, a heater elementmounted on said supporting structure, a tubular getter member positionedaround said heater element, and a plurality of annular getter memberspositioned around said tubular getter member in an axially spacedstacked array.

7. A getter device according to claim 6, wherein said annular membersinclude longitudinally extending outer rim portions efiective forminimizing heat radiation and outward migration of volatile materialsfrom between said annular members.

8. A getter device according to claim 6, wherein said tubular gettermember and said annular getter members comprise a metal selected fromthe group consisting of titanium, zirconium and hafnium and combinationsthereof.

9. A getter device comprising a longitudinally extend ing heater elementwith an electric terminal at each end and an electric terminalintermediate the ends dividing said heater into two portions, a firsttubular getter member substantially coextensive with one of said twoportions of said longitudinally extending heater elements and positionedabout it, and a second tubular getter member substantially coextensivewith both portions of said longitudinally extending heater element andpositioned about said heater element and said first getter member.

10. A getter device according to claim 9, wherein an end cap of gettermaterial is provided on one end of said first tubular getter member.

References Cited by the Examiner UNITED STATES PATENTS 6/40 De Boer eta1 313-176 5/49 Beers 313180

1. A GETTER DEVICE COMPRISING IN COMBINATION, A PLURALITY OF GETTERMEMBERS, AN INDEPENDENT HEATER ELEMENT FOR SAID GETTER MEMBERS, ONE OFSAID GETTER MEMBERS INTERPOSED BETWEEN SAID HEATER ELEMENT AND ANOTHEROF SAID GETTER MEMBERS IN HEAT SHIELDING RELATIONSHIP THERETO WHEREBYSAID ONE GETTER MEMBER WILL BE HEATED TO A HIGHER TEMPERATURE THAN SAIDOTHER GETTER MEMBER TO GETTER A GAS NOT GETTERED BY SAID OTHER GETTERMEMBER AT A LOWER TEMPERATURE.